The friendship between the Mercedes team-mates turned into enmity last season as Hamilton beat his rival to the world drivers' title.

This season, their relationship was simmering as Hamilton dominated the proceedings at the start of the campaign, but the conflict has again spilled over into the public arena after the China Grand Prix.

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Chinese GP: Nico Rosberg criticises 'slow' Lewis Hamilton

Hamilton won the race but Rosberg, who came second, accused his team-mate of not going as fast as he could in order to deliberately back him up into third-placed Sebastian Vettel, of Ferrari.

"Interestingly, he said he was just thinking about himself and that says it all," said Rosberg.

"What upsets me is that my race was massively compromised and we went through that scenario before the race.

"It was always very close with Vettel coming out of the pits and that was completely unnecessary risk to put me in because we had a pace advantage over him."

Hamilton and Rosberg show their emotions after the China Grand Prix

Hamilton denied the claim but the battle on and off the track between the two is now back on.

BBC Sport's David Coulthard:

"It's a frustration for Nico. Lewis tells us he was racing as hard as he could do and we have to take him at face value. It may well be the little bit of anger Nico needs."

And BBC Sport looks back at the Hamilton-Rosberg acrimony for the 2014 title which, fittingly, began nearly a year ago...

Warning signs

It surely had the makings of the perfect partnership. Childhood friends racing for a team that expected to be challenging for the 2014 championship.

The two are involved in a thrilling duel at the Bahrain Grand Prix in April, with Hamilton coming out on top to win his second race of the year.

Rosberg, though, is not happy with the way his team-mate's victory, claiming the Englishman's move on the 18th lap was "over the line".

The German later plays down any disharmony between the team-mates, adding: "It is not the first time we've had a battle, or the first time it's been a little bit close. We have had so many, right back to 12 years old."

Team radio

Rosberg: "Someone needs to tell Lewis that that move was NOT ON!"

Paddy Lowe, Mercedes executive director (technical), to Hamilton: "Ten laps left to race. Let's just make sure we bring both cars home."

Hamilton adds: "It was a bit more like a go-kart race. I hope there are more races like that through the year."

Cracks appear

The comments about each other become increasingly heated as the 2014 season wears on.

It is his fourth victory in succession and moves him to the top of the championship standings, three points ahead of Rosberg.

After the race, Hamilton says he needs to find a way to break his team-mate's mental strength.

It is a comment that appears to irk Rosberg, who retorts: "Break me down mentally? I think he will struggle with that one."

Coming to a head

Previous on-track tussles and wars of words may have been playfully batted away, but the first real sign of tension between the two comes in Monaco after Rosberg secures pole in controversial circumstances.

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Monaco Grand Prix: Nico Rosberg causes controversy in qualifying

After clocking the fastest lap, Rosberg goes off at the Mirabeau corner. Track officials wave the caution flags to slow the cars still out on the track, denying Hamilton the chance to his improve his best time and challenge for pole. The 2008 world champion is furious.

"This weekend went in a direction I wasn't expecting," says Hamilton following Rosberg's victory.

Hamilton later tells BBC Radio 5 live: "People are always talking about friends, I can count my friends on one hand. I am sure Nico can do the same. I am not in his five and he is not in my five.

"The rest does not matter. We are here to win and here to race, we have a great amount of respect for each other, that is all we need."

Mercedes boss Niki Lauda

"The tension is building up, no question, but the team has to make sure the tension does not get out of hand."

Hamilton was furious after qualifying for the Monaco Grand Prix.

Friends again

What better way to patch up your differences than on social media? As Hamilton takes to Twitter to reminisce about his long-standing relationship with Rosberg.

Hamilton and Rosberg back in their karting days

"We've been friends a long time & as friends we have our ups and downs," Hamilton wrote on 30 May: "Today we spoke and we're cool, still friends #no problem."

Lewis Hamilton on 20 July, following the German Grand Prix: Congrats to Nico winning home race! This c'ship is proving a big challenge but that's how I love it - and I wouldn't have it any other way!

Hungary for more

The niceties do not last for long, though, as the pair go head-to-head again in Hungary. Rosberg is left furious after Hamilton refuses to follow team orders and allow him to pass.

Team radio

Engineer to Hamilton: "OK Lewis, if you let Nico past please. Let him through on the main start/finish straight."

Hamilton: "I'm not slowing down for Nico. If he gets close enough to overtake, he can overtake me."

Rosberg: "Why is he not letting me through?"

Hamilton admits he is "very, very shocked" by the request to allow his team-mate through. He eventually takes third place, with Rosberg finishing fourth.

The German refuses to discuss the incident publicly after the race.

BBC Sport's David Coulthard:

"I think Hamilton is doing what he should do, His exact words were, 'I am not slowing down for Nico', which is right, why should he slow down when he is racing? Nico is just not doing enough."

'Nico hit me, he just hit me'

The mid-season break does little to alleviate any tensions between the two drivers and things come to a head in Spa when the German effectively ends Hamilton's race on only the second lap of the Belgian Grand Prix.

Having locked out the front row with Rosberg on pole, Mercedes are in prime position for a one-two finish.

Those hopes are ended quickly, though, when Rosberg punctures Hamilton's left rear tyre when he hits the back of his team-mate's car at the start of lap two.

Hamilton's shock at the incident is evident when he yells over the team radio: "Nico's just hit me, he's just hit me."

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Rosberg clips Hamilton in Belgian GP

After the race, the two drivers meet Mercedes officials to discuss what happened.

"We had a meeting about it and he basically said he did it on purpose," an incredulous Hamilton reveals.

"He said he could have avoided it, but he didn't want to. He basically said, 'I did it to prove a point'."

"Lap number two of a long race, a crash between two team-mates," he says. "It is absolutely unacceptable."

After the team's post-race debrief, Wolff adds: "They agreed to disagree in a very heated discussion among ourselves, but it wasn't deliberately crashing. That is nonsense."

Cracking under pressure

With the German in the spotlight after being criticised by his team for causing the collision at Spa he makes a costly mistake under pressure from Hamilton to hand his team-mate victory in Italy.

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Lewis Hamilton takes lead after Nico Rosberg error

Having taken pole in qualifying, a glitch in Hamilton's start procedure sees him drop to fourth early on and Rosberg takes the lead in Monza.

The Briton battles back and looms large in the mirrors of his team-mate. Under pressure, Rosberg brakes too late into the first chicane and is forced to take to the escape road for the second time as Hamilton takes the lead and holds it to the chequered flag to reduce his deficit in the title race to 22 points.

Roseburg, who finishes second and is once again booed on the podium, is magnanimous in defeat, saying: "Lewis drove a great race and he deserves it today."

BBC Sport's David Coulthard:

"Lewis has beaten Nico psychologically after what happened at Spa, when Nico was chastised for what he did. Now, every time they're in a wheel-to-wheel situation, he has Nico beaten. He knows he is the better racer."

He says: "It has changed from, let's say, an almost amicable relationship at the beginning of the season to a very intense moment, where it was almost like realising these two are enemies competing for the world title."

Ghost in the machine

Hamilton wins in Singapore to take a three-point lead in the drivers' championship after Rosberg retires with an electrical problem.

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Rosberg's Singapore GP woe

The German has trouble with gear selection issues from the moment he tries to leave the garage before the race.

Rosberg changes his steering wheel and has to start from the pit lane while Hamilton powers away from pole position to claim his seventh win of the season and superiority in the Mercedes rivalry.

Both drivers have now suffered two retirements as a result of mechanical failure.